Resumo. Aiming at contributing to the knowledge of physical factors affecting community structure in Atlantic Forest remnants of southern Bahia state, Brazil, we analyzed the annual variation in the understory microclimate of a hillside forest fragment in the ‘Reserva Particular do Patrimônio Natural Serra do Teimoso’ (RST) and a rustic cacao agroforestry system (Cabruca), located nearby the RST. Canopy openness (CO), air temperature (Ta), air relative humidity (RH) and vapor pressure deficit (VPD) data were collected between April, 2005 and April, 2006 at the base (RSTB, 340 m) and the top (RSTT, 640 m) of the RST and at the Cabruca (CB, 250 m). Data of rainfall, Ta, RH and VPD were also collected in an open area (OA, 270 m). The highest rainfalls (> 100 mm) occurred in November, 2005 and April, 2006, whereas October, 2005 was the driest month (< 20 mm). CO ranged between 2.5 % in the CB (April, 2006) and 7.7 % in the RST (October, 2005). Low rainfall in October, 2005 affected VPDmax in all sites. Those effects were more pronounced in OA, followed by CB, RSTB and RSTT. During the period of measurements, the values of Ta, RH and VPD in CB were closer to the values measured in OA than to the values measured inside the forest.